Even if they don't, it's a matter of being a bit quick and resourceful. If you have sufficient time it should not be a problem (depending on thr airport).
Same thing happened to me at Schiphol with a rather expensive Leatherman Tool. Went back out, down to the newspaper stand and brought a boatload of postage stamps. They were even kind enough to give me a free envelope (otherwise I was going to wrap it in a sheet of paper). Dropped it in the mailbox and went back, took perhaps 15 minutes in all. Needless to say a very strange letter but was lying in the mailbox when I got back.